Solar cells having graded doped regions and methods of making solar cells having graded doped regions

Abstract

A photovoltaic cell having a graded doped region such as a graded emitter and methods of making photovoltaic cells having graded doped regions such as a graded emitter are disclosed. Doping is adjusted across a surface to minimize resistive (I2R) power losses. The graded emitters provide a gradual change in sheet resistance over the entire distance between the lines. The graded emitter profile may have a lower sheet resistance near the metal lines and a higher sheet resistance farther from the metal line edges. The sheet resistance is graded such that the sheet resistance is lower where I2R power losses are highest due to current crowding. One advantage of graded emitters over selective emitters is improved efficiency. An additional advantage of graded emitters over selective emitters is improved ease of aligning metallization to the low sheet resistance regions.

Description

BACKGROUND[0001]1. Field[0002]This invention relates to the art of methods for making solar cells and, more particularly, to solar cells having graded doped regions and methods of making solar cells with graded doped regions. Doped regions can include emitters and surface fields.[0003]2. Related Art[0004]Solar cells, also known as photovoltaic (PV) cells, convert solar radiation into electrical energy. Solar cells are fabricated using semiconductor processing techniques, which typically, include, for example, deposition, doping and etching of various materials and layers. Typical solar cells are made on semiconductor wafers or substrates, which are doped to form p-n junctions in the wafers or substrates. Solar radiation (e.g., photons) directed at the surface of the substrate cause electron-hole pairs in the substrate to be broken, resulting in migration of electrons from the n-doped region to the p-doped region (i.e., an electrical current is generated). This creates a voltage diff...

AI Technical Summary

Benefits of technology

The invention provides a photovoltaic cell with a graded doping region and metal contacts. The graded doping region has a gradual change in sheet resistance over the distance between adjacent metal contacts to optimize the distribution of electrical current. The method of making the photovoltaic cell involves ion implantation or plasma immersion doping. The technical effect is improved performance and efficiency of photovoltaic cells.

Problems solved by technology

The resistive power loss increases as the square of the current in the emitter.

Since the power loss is P=I2R, the increase in current near the metal contact increases the resistance power loss as the square of the current.

However, doing so increases the recombination and optical losses in the emitter.

Unfortunately, low sheet resistances increase recombination losses, reducing Voc, and optical losses, reducing Jsc.

Selective emitters have a uniform sheet resistance between the metal fingers, and, therefore exhibit higher I2R power losses which counter diminish the benefits of lower recombination losses in the high sheet resistance regions.

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